This Non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2003-311484 filed in Japan on Sep. 3, 2003, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an inkjet recording apparatus and image forming method, and more particularly to an inkjet recording apparatus equipped with a recording head having nozzle rows in which a plurality of nozzles serving as ink ejection ports are arranged, and to an image forming method thereof.
2. Description of the Related Art
Inkjet recording apparatuses have an inkjet head (print head) in which a large number of nozzles are arranged, and form images on a printing medium such as recording paper by ejecting ink from the nozzles while moving the print head and the printing medium relatively to each other. In such inkjet recording apparatuses, there are cases in which some of the large number of nozzles no longer eject ink for some reason, the amount of ink ejected (the dot size resulting from the ejection of an ink-droplet on the recording paper) or the flight direction of the ink-droplet (i.e., ink-droplet deposition position) becomes defective, and other ejection defects occur. The defective ejection of such nozzles causes the quality of the recorded images to be degraded. In the present specification, displacement from the ideal state related to the dot position, dot size, dot shape, dot density distribution, and the like due to defective ejection from nozzles is referred to as “locality of nozzles” or “nozzle locality”.
Inkjet recording apparatuses operate using a shuttle-scan method whereby images are formed as the recording head reciprocates in a direction (main scanning direction) substantially perpendicular to the conveyance direction of the print medium, and a one-pass (single pass) method whereby images are formed by a single conveyance of the medium alone in the sub-scanning direction using a full-line recording head having a nozzle row that covers the entire width of the print medium in the main scanning direction. Each of these methods handles a locality of nozzles in a different manner.
In the case of the shuttle-scan method, dots can be formed by ink-droplet ejection from different nozzles on the same sub-scanning line or in the vicinity thereof because the recording head reciprocates in the main scanning direction. In other words, the locality of nozzles is dispersed by multiple passes in the shuttle-scan method, and dot placement in which streak-type nonuniformity or the like is visually less noticeable can be realized.
In contrast, the recording head is fixed in the one-pass method, so that it is impossible to disperse the locality of nozzles through head movement as with the above-described multiple passes. There is hence a drawback in that nonuniformity in the form of lines can be visually detected and the image quality is markedly degraded.
Japanese Patent Application Publication No. 2002-234216 discloses, with respect to the drawbacks that are unique to the one-pass method, art that determines the locality of nozzles and determines a dot control value so that displacement is visually less noticeable with consideration for the locality of nozzles (mainly positional displacement and color value displacement) during digital halftoning. In Japanese Patent Application Publication No. 2002-234216, digital halftoning is carried out with consideration for the locality of nozzles, and dots are ejected with minimum visible variation by controlling the driving action of the print head in accordance with the results thereof as shown in FIG. 26, so that dot deposition in which the visibility of nonuniformity is inhibited in accordance with the results.
Nevertheless, in the case of the method disclosed in Japanese Patent Application Publication No. 2002-234216, the dot control value is determined with the content of the image to be printed taken into account, and calculations in which the nozzle locality and the appearance of the image are constantly taken into consideration must be carried out. There is therefore a drawback in that the constant calculating load is considerable, and the memory capacity must be expanded.